Electron Bombarded Semiconductor Device

Abstract

An electron bombarded semiconductor amplifier including an elongated envelope having an electron gun at one end to project an electron beam along said envelope, reverse biased semiconductor diodes forming a target at the other end of the envelope disposed to receive said beam and deflection means for deflecting the beam whereby more or less of the beam strikes the diodes forming the target.

Description

BACKGROUND OF THE INVENTION

This invention relates to amplifiers and more particularly to an electron bombarded semiconductor amplifier.

Electron devices with semiconductor targets are known. However, such devices have been relatively low power, low frequency devices. The deflection means for the beam were primarily suitable for low frequency signal inputs.

SUMMARY OF THE INVENTION AND OBJECTS

It is a general object of the present invention to provide an electron bombarded semiconductor device incorporating improved laminar flow electron gun, beam deflection means and an improved semiconductor target.

It is another object of the present invention to provide a highly efficient, highly linear broad band electron bombarded amplifier.

The foregoing and other objects of the invention are achieved by an amplifier having an elongated envelope with a laminar flow electron gun projecting a longitudinal electron beam disposed at one end of the envelope, semiconductor diodes disposed at the other end of said envelope to form a target for said beam means, a delay line disposed between the gun and target in cooperative relationship with said beam to deflect the beam, and means for applying a signal to one end of the delay line whereby it travels along the line in synchronism with the electron beam to deflect the beam and control the amount of the beam which impinges upon the semiconductor diodes forming the target. The invention also incorporates an improved target configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view in section showing an electron beam semiconductor device in accordance with the invention.

FIG. 2 is a plan view of the delay line beam deflection circuit.

FIG. 3 is an end elevational view of the delay line shown in FIG. 2, taken along line 3--3 of FIG. 1.

FIG. 4 is a front view showing the semiconductor target assembly of the present invention taken along the line 4--4 of FIG. 1.

FIG. 5 is a sectional view of the target assembly.

FIG. 6 shows a preferred semiconductor diode target.

FIG. 7 is a sectional view taken along the line 7--7 of FIG. 1 showing the mask disposed in front of the target.

FIG. 8 is a drawing of an RF lead-through for connecting to the diode target.

FIG. 9 is a schematic circuit diagram showing a single diode connected in a Class A amplifier.

FIG. 10 shows the output voltage waveform at the load with linear deflection of the beam for the circuit shown in FIG. 9.

FIG. 11 is a schematic circuit diagram showing two diodes connected in a Class B amplifier circuit.

FIG. 12 shows the output voltage waveform at the load with linear deflection of the beam for the circuit shown in FIG. 11.

FIG. 13 shows a semiconductor diode target with integral bypass capacitors.

FIG. 14 is a schematic circuit diagram of the device shown in FIG. 13.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIG. 1, a laminar flow sheet electron beam is formed by the electron gun 11. This beam is projected along the tube envelope 12 through a deflection structure 13 which imparts vertical motion to the electron beam due to the electric fields between its upper and lower conductors 14 and 16. This is followed by a drift space 17, beyond which is located the semiconductor target assembly 18. The beam deflection at the targets is proportional to the voltage applied to the input of the deflection structure. Reverse biased semiconductor diodes form the target. The target assembly and diodes will be presently described.

When the diodes are bombarded by the incident electrons, hole-electron pairs are created within the reversed bias diode. The internal electric fields due to the reverse bias cause either holes or electrons, or both, of these carriers to flow through the diode and through the external load Z.sub.L, FIGS. 9 and 11.

The incident velocity with which the beam electrons strike the target is typically chosen to be between 10 and 20 kV. For each electron entering the target, a current multiplication takes place which is approximately 2,000:1 at 10 kV and 5,000:1 at 20 kV. The current flow in the targets is then proportional to the electron beam current striking the target. This basic property of the device leads to its linear amplification properties. A single diode target is suitable for use as a Class A amplifier or as a d.c. pulse amplifier. Twin targets such as shown in FIGS. 4, 5 and 13 are suitable for use as Class B RF or video amplifiers. The manner in which the diode targets are connected to the load is shown in FIGS. 9 and 11 for Class A and Class B operation. A Class A device is a simple series connection of a d.c. voltage source V.sub.bb, the semiconductor diode 21 and the resistive load Z.sub.L. The load is typically a coaxial line or microstrip transmission line terminated in its characteristic impedance. The source voltage V.sub.bb divides itself between a voltage drop across the diode V.sub.ST and a voltage drop across the load V.sub.L. In a Class A device, the electron beam is given a quiescent position which illuminates one-half the diode. This gives a resulting quiescent current which is one-half of the peak current flowing during a deflection cycle.

The Class B device, FIG. 11, consists of two Class A circuits connected to a common load Z.sub.L. The spacing between the two diodes in the target is arranged so that the quiescent position of the beam lies between the two targets and, ideally, no current flows unless the beam is deflected. Deflecting the beam to the upper diode causes a current to flow so that the positive polarity of the voltage V.sub.L is developed across the load. Deflecting the beam onto the other target causes the opposite polarity to be developed. Current flowing in the diode at any instant of time is directly proportional to the amount of beam incident on the diode. Thus, there is a linear relationship between the beam deflection and the output voltage V.sub.L generated across the load. The ideal Class B device has the advantage that no current flows through the load when the beam is in its undeflected position. For purposes of simplicity, the remainder of the description will be directed to Class B type devices.

The electron gun 11 serves to develop a sheet beam which is directed along the envelope towards the rectangular diode targets. The electron gun includes an indirectly heated strip cathode 26 for emitting electrons, an apertured electrode 27 which serves as the grid and is closely adjacent to the strip cathode 26. An anode is spaced from said cathode electrode and cooperates therewith to provide a substantially uniform electric field at the surface of the cathode strip. Electrons emit normal to the entire cathode surface in a flat or sheet beam. The anode also forms a divergent electrostatic lens along the path of the beam. Accelerating and focusing means in the form of an electrode 29 disposed further along the path of the beam accelerate and focus the beam towards the semiconductor targets. The members 31 and 32 serve to provide a field-free region for the beam to drift to the deflection structure 13. A suitable electron gun is described in copending application, Ser. No. 149,445, filed June 3, 1971, entitled "Laminar Flow Electron Gun and Method."

The upper plate 14 of the deflection system 13 is in the form of a meander line which defines a travelling wave deflection structure. The meander line is in the form of a sheet or plate which includes slots 15a, 15b extending inwardly alternately from opposite sides to form the structure. This eliminates electron transit time, and high frequency deflection limitations. It is a constant impedance, constant phase velocity 50 ohm line disposed above the ground plane 16. It is driven from a coaxial input connector 30 and the far end of the line is brought out through another coaxial connector 35 to an external termination, or terminated internally. For maximum deflection sensitivity, the spacing between the meander line 14 and the lower ground plane 16 increases with distance down the length of the tube. This prevents beam interception of electrons as the electron beam deflection increases toward the far end of the line. In the region where deflection is zero, at the input end of the line the spacing can be less which leads to increased deflection sensitivity at the input end of the structure. Alternatively, for somewhat reduced deflection sensitivity, the initial spacing is increased and tapering of the spacing is not necessary. The line is substantially wider than the electron beam with which it interacts thereby providing a more constant electric field to the beam. The increased width provides the desired impedance.

The meander line is supported by a pair of spaced rings 33 and 34 carried in the tube envelope. The rings are each provided with a web 36, FIG. 3, through which extends a pair of spaced rods 37 and 38. The meander line is disposed underneath the rods and is held or supported by the rods by means of tabs 41 which are spot welded to the top of the meander line. The lower plate 16 is supported from the meander line by means of side strips 42 and 43, FIG. 3.

By way of example, the meander line design can be chosen to have a phase velocity which is 0.2 times the velocity of light. This corresponds to a synchronous electron velocity of 10,000 volts. The velocity of the waves on the meander line structure is essentially independent of frequency.

The target assembly 18 is shown in FIGS. 4, 5, 6 and 7. The target assembly includes a support 46 adapted to receive a sealing ring 47, FIG. 1, which is welded to the sealing ring 48 carried by the envelope. The support 46 receives a coaxial conductor 49 to be presently described with its inner conductor projecting into the tube envelope. The support carries a beryllium oxide substrate 51 on which the semiconductor diodes forming the target are mounted. Referring to FIG. 4, diodes 52 and 53 are mounted on metallized areas 54 and 56, respectively. The metallized area 56 is connected by leads 57 to the center conductor of the coaxial input and forms the common terminal. The metallized area 54 is connected to a lead 58 which extends through the support and is sealed thereto as, for example, by means of a sealing ring 59 connected to the ceramic sleeve 60 which surrounds the lead. The other terminal of the diode 52 is connected to the metallized area 56 forming the common connection between the two diodes. The second terminal of the diode 53 is connected to a metallized area 61 and thence to an input lead 62 which extends through the support and is sealed as described above. The beryllium oxide substrate is metallized around the entire outer surface as shown at 63. This surface is connected to the outer conductor of the coaxial lead to maintain the area at ground potential. This also acts as the ground return for the d.c. supply. A mask 64, FIG. 7, is mounted on the front wall of the mount 46 by means of screws 66. The mask is provided with a pair of spaced windows 67 and 68 which expose only the active area of the diodes 52 and 53 to the electron beam.

The diodes 52 and 53 may be formed by ion implantation on bulk material or by diffusion into epitaxial material. Referring to FIG. 6, N-type silicon 71 is bonded directly to a high thermal conductivity N+ substrate 72. The upper surface includes a silicon dioxide layer 73 which is provided with a window 74 through which is formed a P-type region 76. An aluminum metal overlay 77 provides the contact to the other terminal of the diode. The aluminum metal layer is sufficiently thin so that it can be penetrated by the electron beam to form the secondary electrons within the bulk of the diode near the P-N junction.

The RF connection 49 may be of the type shown in FIG. 8 and include a body portion 81. A window support 82 placed in the upper bore of the member 81 extends upwardly to receive metallized window 83. The lower portion of the window receives the pin assembly 84 which extends upwardly to provide the coaxial interconnection and extends downwardly concentric with the metallic tube 86 and is maintained in spaced relationship by a ring 87.

A target assembly 18 including bypass capacitors is shown in FIG. 13 and the equivalent circuit is shown in FIG. 14. Since the target is substantially the same as that shown in FIG. 4, the same reference numerals are applied to like parts. The target assembly includes a beryllium oxide substrate 51 on which the semiconductor diodes forming the target are mounted. Referring to FIG. 13, diodes 52 and 53 are mounted on metallized areas 54 and 56, respectively. The metallized area 56 is connected by leads 57 to the center conductor of the coaxial input and forms the common terminal. The metallized area 54 is connected to a lead 58 which extends through the support and is sealed thereto as described above. The other terminal of the diode 52 is connected to the metallized area 56 forming the common connection between the two diodes. The second terminal of the diode 53 is connected to a metallized area 61 and thence to an input lead 62 which extends through the support and is sealed thereto. The beryllium oxide substrate includes a third metallized area 91 connected to the outer conductor of the coaxial lead. This area extends under metal members 92 and 93 each of which forms one plate of a capacitor and serves to form the other plate. A dielectric, not shown, is disposed between the plates. Leads 94 connect to the areas 54 and 61. Referring to FIG. 14, the capacitors are shown at 96 and 97. The capacitors provide for higher frequency operation of the amplifier.

In conclusion, we have shown a new type of RF amplifier which exhibits low pass amplifier characteristics and can operate from d.c. up to some predetermined cutoff frequency. In contrast to most microwave vacuum tube amplifiers, its dimensions do not grow inversely with frequency. Compact, light-weight amplifiers can be designed and built which have power output capabilities up to several kilowatts. One of the most significant characteristics of this device is its efficiency capability. The absence of the required magnetic focusing field greatly reduces the weight, size and complexity of the device.

Claims

We claim:

1. An electron bombarded semiconductor device comprising an evacuated envelope, an electron gun positioned at one end of said envelope to project an electron beam along said envelope in a predetermined path, means comprising a delay line positioned along said beam to interact with said beam, means for applying a signal to one end of said delay line whereby it travels along the line to interact with the beam to deflect the beam from the predetermined path responsive to a signal applied to said line, a semiconductor target comprising a pair of spaced diode devices each having first and second regions forming a p-n junction with one region adapted to receive said beam, with the beam impinging between said devices when it is in said predetermined path and striking said one region of one or the other of said devices when deflected responsive to an input signal, means for interconnecting one region of said devices, a load having one terminal connected to said interconnecting means, and means for applying a voltage between the other terminal of said load and the other region of each of said devices to reverse bias the semiconductor diode devices.

2. A device as in claim 1 including a mask disposed in front of said diodes whereby the beam strikes said diodes only when it is deflected.

3. A device as in claim 1 wherein said slow wave structure comprises a meander line spaced from a ground plane.

4. A device as in claim 3 wherein said meander line comprises a plate having slots extending inwardly alternately from opposite sides.

5. A device as in claim 4 including a ground plane spaced from said plate with the spacing increasing in the direction of the target.

6. A device as in claim 1 including a non-conductive support, conductive pads formed on said support to receive said diode devices and form a connection with one terminal of each device, a conductive film spaced from said pads and forming a ground adapted to be connected to the other terminal of said load, a coaxial conductor having its outer conductor connected to said ground and its inner conductor to a terminal of each of said diode devices to form the interconnection and adapted to be connected to said one terminal of said load and means providing electrical connection to each of the other terminals of said diode devices for applying said voltage.

7. A device as in claim 6 including capacitors carried by said support and connected between the conductive film forming ground and the means providing electrical connection to the other terminals.